1. Stubbornly adhering to an attitude, opinion, or course of action; obdurate.
2. Difficult to manage, control, or subdue; refractory.
3. Difficult to alleviate or cure: an obstinate headache.

Synonyms: These adjectives mean tenaciously unwilling to yield. Obstinate implies unreasonable rigidity: "Mr. Quincy labored hard with the governor to obtain his assent, but he was obstinate" (Benjamin Franklin).
Stubborn pertains to innate, often perverse resoluteness or unyieldingness: "She was very stubborn when her mind was made up" (Samuel Butler).
One who is headstrong is stubbornly, often recklessly willful: The headstrong teenager ignored school policy.
Stiff-necked implies stubbornness combined with arrogance or aloofness: The stiff-necked customer irked the cashier.
Bullheaded suggests foolish or irrational obstinacy, and pigheaded, stupid obstinacy: Don't be bullheaded; see a doctor. "It's a pity pious folks are so apt to be pigheaded" (Harriet Beecher Stowe).
Mulish implies the obstinacy and intractability associated with a mule: "Obstinate is no word for it, for she is mulish" (Ouida).
Dogged emphasizes stubborn perseverance: dogged persistence; "two warring ideals in one dark body, whose dogged strength alone keeps it from being torn asunder" (W.E.B. Du Bois).
Pertinacious stresses a tenacity of purpose, opinion, or course of action that is sometimes viewed as vexatious: The tax bill's vocal and pertinacious critics led to its defeat.